The investigation into the death of Ian Tomlinson will inevitably lead to an independent inquiry, lawyers say. And they believe new evidence obtained by the Guardian means the case must be referred to the Crown Prosecution Service to consider whether criminal charges should be brought against any police officers.

Tomlinson's death during the G20 protest in the City of London is already under investigation. But the Independent Police Complaints Commission, which is responsible for considering serious incidents or allegations of misconduct, has said that it is not yet carrying out its own inquiry but managing one being undertaken by the City of London police.

"If there are allegations that the death was caused or contributed to by unlawful actions of the police, then a police investigation would not be satisfactory," said Harriet Wistrich of Birnberg Peirce, the solicitors who represented the family of Jean Charles de Menezes.

"The IPCC should clearly run its own independent investigation which could lead to a referral of the case to the Crown Prosecution Service to decide whether to bring a criminal prosecution against the officers.

"If there is evidence of an assault, even if there is evidence to suggest there was a lawful defence to the assault, then it has got to be referred to the CPS."

The conduct of investigations into fatal police incidents has been under scrutiny since the death of De Menezes, who was shot by police at Stockwell tube station in 2005. In that case, an IPCC report identified serious weaknesses in the Metropolitan police's handling of critical information.

Experts fear that crucial evidence from the scene of Tomlinson's death may have been overlooked. "Speed is of the essence," Nick Bowen, a barrister, said. "It is absolutely vital that the IPCC approach every investigation of this nature with a completely open mind. In the De Menezes case, they appear to have leapt to certain conclusions presumably on the basis of information that was provided to them by the police, which they should have been sceptical about."

"If an IPCC investigation is going to be effective, then its investigators should be at the scene of the incident ensuring that evidence is preserved at the very earliest opportunity," said Jules Carey of Tuckers solicitors, who has handled a number of police complaint cases. "Cases are solved by effective early action and in this case the golden hour is long passed."

Critics say recent decisions not to prosecute officers, including the De Menezes case where the CPS decided not to charge individual officers despite the fact that the inquest jury disbelieved key parts of the officers' accounts, suggest a prosecution in the latest instance is unlikely.

Figures obtained by the charity Inquest show that in cases where an inquest has delivered a verdict of unlawful killing, there have been only seven prosecutions of officers since 1990. "If you look at the record of cases where somebody's death has been caused by actions of the police, there have been hardly any prosecutions brought," Wistrich said. "The record is really, really poor.

Questions are also being asked about the conduct of the police in the aftermath of the investigation, when contact between Tomlinson and the police - now clearly shown on the footage obtained by the Guardian - was strenuously denied.

"It is likely that there will be evidential difficulties because the incident was not promptly, immediately and independently investigated," Bowen said. "Information about the identification of the officers involved and crucial evidence relating to who may have struck Mr Tomlinson may have been lost."

As well as the potential for losing time-sensitive evidence, concerns have been raised that initial responses denying Tomlinson's contact with the police may have been misleading.

"An IPCC report on the de Menezes case was critical of what they identified as serious weaknesses by the Metropolitan police in the handling of critical information in the immediate aftermath of the Stockwell shooting," Carey said.